High-frequency alternator



E. F. w. ALEXANDERSON.

HlGH FREQUENCY ALTERNATOR.

APIILXCATION mso SEPT. 23. 1916.

1,426,943, Patented L 1 22, 1922.

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' Inventor:

Ernst, FW.A|exanderson,

H is Attorneg.

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Patented Aug. 22, 1922.

Inventor: Ernst FWAlexancterson,

E. F. W- ALEXANDERSON.

HIGH FREQUENCY ALTERNATOR.

APPLICATION FXLED SEPT. 23. I916.

b MAMQM His Attorney- E F. W. ALEXANDERSON.

HIGH FREQUENCY ALTERNATOR.

APPLICATION FILED SEPT, 23, I916.

faiel'lted Aug. 22, 1922.

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WUJ mwe s m w w r t on A a n s x n. F a m E E. F. w. ALEXANDERSON.

HIGH FREQUENCY ALTERNATOR.

' I APPLICATION FILED SEPT.23, I9IB.

1,426,948,, Patented 22, 1922.

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ventor Ernst F. .7 \lexander-son His "Attorneg- UNITED STATES ERNST I. W. ALEXANDERSON, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL PATENT OFFICE.

- ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HIGH-FREQUENCY ALTERNATOR.

Specification of Letters Patent. Patented Aug. 22, 1922.

Application filed September 23, 1916. Serial No. 121,870.

To all to ham it may concern Be it known that I, ERNST F. W; ALEX- ANDERSON, a citizen of the United States, residing at Schenectady, in the countyof Schenectady, State of New York, have invented certain new and useful Improvements in Hi h-Frequency Alternators, of which the fol owing is a specification.

My invention relates to alternators for generating alternating current of high frequency, and more particularly to radio frequency alternators, and has for its object the provision of an improved high fre-' quency alternator of the inductor type.

I have heretofore described in United States Letters Patents No. 1,008,577,- patented November 14, 1911, and Nos. 1,110,028, 1,110,029 and 1,110,030, patented September 8, 1914, high frequency alternators ofthe inductor type. In the alternators of my prior patents the inductor or rotor is of solid steel made in the form of a disc designed for maximum strength with respect tocentrifugal forces. The disc is provided near its periphery with a plurality of radially dis posed slots, so as to provide a plurality of magnetic poles for the inductor. In order to avoid excessive windage at the high speeds at which the inductor is designed to operate, the slots in the inductor periphery are filled with solid non magnetic blocks. The magnetic poles of the inductor are thus formed on both sides of this disc-shaped element, and it is necessary to provide equalizing means for the thrust bearings of the inductor shaft, in order to maintain the inductor centrally located in the active air-gap of the machine. One form of such equalizing means is described in Patent, No. 1,110,030.

The improved alternator of my present invention is in principle of substantially the same type as described in my prior patents. The inductor of the improved alternator, while generally disc-shaped and designed for maximum strength with respect to cen trifugal forces,has, however, a cylindrical peripheral surface upon which magnetic poles are adapted to be formed. The active air gap of the improved alternator is thus between the peripheral cylindrical surface of the inductor and the adjacent laminated stator member in which is carried the armature windin arranged in suitable slots. I have devise several forms of this imp ed scription taken in conjunction with the accompanying drawings, in which;

Flg. 1 1s a vertical cross-section of the upper half of a high frequency alternator embodying my present invention; Fig. 2 is a detail and elevation of the inductor showing the arrangement for producing magnetic poles on the cylindrical peripheral surface; F igs. 3 to 14: are vertical cross-sections of the upper half of high frequency alternators embodying my invention in other modified forms; and Fig. 15 is a detail View ofa typical laminated armature core and wind ing employed in my improved alternator.

In each of the figures of the drawings, the I main stator frame is of magnetic material, such as iron, and is represented by reference character 15. The field winding of each of the alternators shown in the figures of the drawings is made up of one or more ringshaped coils 16 secured within the frame 15, as will be more clearly described hereinafter, The armature winding 17 is carried in suitable slots on the inner cylindrical surface of an annular laminated magnetic memher 18, (Fig. 15), which I will hereinafter call the laminated armature core. In the various modifications shown in the drawings, the armature cores 18 are of different widths, but are otherwise of substantially the same design. In each of the machines shown in" the drawings, the inductor or inductors are mounted on a rotatable shaft 19. and aresecured in position thereon by nuts 20. v

Referring now more particularly to Fig. 1 ofthe drawings, it will be observed that the field coil 16 is mounted between two flared near its periphery so as to provide a cylindrical peripheral surface of the desired width. Dove-tailed slots are cut on the pe ripheral surface of each inductor, thereby providing a pluralit of teeth 2 i-integral with the inductor an adapted to form magnetic poles, in the well understood manner. The slots between the teeth 24 are filled with solid non-magnetic blocks 25, so as to reduce the windage at the very high speeds. at

which the inductor is designed to rotate.

The blocks 25 may be of aluminum or other suitable material, and are preferably forced into the slots and riveted in place so as to fill the slots flush with the adjacent surfaces of the inductor, as indicated in Figs. 1 and2 of the drawings.

The change in the flux density surrounding the armature conductors occasioned by the rapidly revolving magnetic poles of the inductor induces alternating current of high frequency in the armature winding, as is well understood in the art. The flux produced by the exciting or field coil 16 passes through the frame 15 into one of the members 21 and then through the laminated armature core 18 across the active air gap into one of the inductors 23 and then to the other inductor 23 and across the other active air gap into the core 18 and member 21 and back to the frame. The width of the peripheral surface of the inductor is limited by the required design for maximum strength, and in order to increase the output of the machine I may arrange two or more inductors in parallel, so that the cylindrical surfaces of the several disc inductors are adjoining, as shown in Fig. 3.

In the machines shown in Figs. 1 and 3, it will be evident that two inductors are necessary in order to complete the magnetic circuit for the exciting flux. Since the flux passes across the active air gap of one inductor, or set of inductors in the case of Fig. 3, in one direction and across the active air gap of the other-inductorin the opposite direction, it will be understood that the magnetic poles of one inductor, or the slots for the armature conductors in one laminated core 18, should be displaced 180 electrical degrees from corresponding poles or slots, in the other inductor, or armature core, as the case may be, in order that the currents induced in the armature windings carried in the two cores 18 may be in phase. In the drawings, I have represented the inductor poles displaced by 180 electrical degrees, which means that the non-magnetic filling blocks 25 of one inductor, or set of inductors in the case of Fig. 3, are positioned opposite the magnetic teeth or poles 24 of the other inductor.

In machines of small capacity where it is desirable to employ only a single inductor, the magnetic circuit can be completed through stationary magnetic members instead of through a second inductor. This modification of the invention is illustrated in Fig. 4. Stationary circular lates 27 of magnetic material are suitab y mounted near the ends of the frame 15. Each plate 27 surrounds the shaft 19, and is separated .by as small an air gap as is mechanically operating two inductors in parallel on the shaft 19, as illustrated in Fig. 5. Fig. 6 illustrates a machine, of the type represented in Fig. 3, provided with the stationary magnetic plates 27 of the machines of Figs.

4 and 5. This machine has three exciting coils 16 which cooperate toforce flux across the active air gap of one pair of inductors in one direction and across the active air gap ofthe other pair of inductors in the opposite direction.

In the machines of Fi s. 1, 3 and 6 half of the inductors are use for returning the flux to the stator, "so that in effect half of the inductors are magnetically in series with the other half, so that inductor poles or armature slots ofone half of the machine must be displaced 180 electrical degrees with respect to the corresponding elements of the other half of the machine. In the machine of Fig. 5, the flux is returned to the stator frame 15 by the stationary magnetic plates 27 sothat the magnetic poles of both inductors, as well as the slots in the armature cores 18, may register, instead of being oil'- set as in themachinesof Figs. 1, 3 and 6.

In all forms of the alternator hereinbefore described, the inductors carry the exciting flux, and must therefore be of sufiicient cross-sectional area to accommodate the flux without saturating. Machines of this type can be satisfactorily designed for peripheral speeds up to about 500 feet per second, but for higher speedsthe required thickness of the inductor disc for the accommodation of the exciting flux is too great for the satisfactory design of the inductor for maximum strength with respect to centrifugal forces. Where it is desired to rotate the inductor at peripheral speeds above about 500 feet per second, I, therefore, provide means for relieving the inductor of the duty of carrying all the exciting flux. One form of this phase of my present invention is illustrated in Fig. 7 of the drawings. As shown in this figure, the inductor 23 has an enlarged portion near. its periphery of generally rectangular cross section. The

outer cylindrical peripheral surface is the frame 15 and extend beneath the inner cylindrical surface of the enlarged peripheral portion of the inductor, and. are separated therefrom by as small an air ap as themechanical design :permits. he armature core 18 is held between the rings 22, while two excitingcoils 16 are mounted between the rings 22 and the L-shaped plates 30. The two exciting coils 16' are so arranged that the fiuxes resulting therefrom pass in the same direction, across the active air gap between the armature core 18 and the slotted peripheral surface of the inductor. It will be evident, that the narrow portion of the disc-shaped inductor carries no flux, and hence the inductor can be designed with special regard to mechanical strength. g

I Fig. 8 of the drawings, a stationary magnetic member 31 of 'T-shaped section is employed for providing a'magnetic circuit between the two inductors 28'. In the alternator of this figure, the two inductorsare in effect arranged in series magnetically, just as in the machine of Fig. 1. The larger portion of the exciting flux passes, however, from one inductor to the other through the stationary T-shaped member 31, and so the inductors need carry as little flux as their design for maximum strength requires.

In Fig. 9 of the drawings, I have shown a machine embodying both the. stationary L-shaped lates 30 and a IT-shaped plate 31. This machine has three exciting coils 16, and it will be observed that the middle coil 16 cooperates with one of the end coils 16 to drive a flux across the active air gap of one inductor in one direction and cooperates with the other end coil 16 to drive .a flux across the active a r gap of the other inductor in the opposite direction. In this machine, there are two paths for the flux in passing from one inductor to the other, first, directly through the two inductors, and, second, through the stationary T- shaped member 31, while in addition a third return path for the exciting flux is provided through the stationary L-shaped memhers-30. I

Fig. 10 illustrates a machine embodying the principles of the machines of Figs. 4, 7 and8. The machine of this figure has four inductors 23 mounted on the shaft 19.

Two of these inductors are magnetically'in parallel with each other and in series with machine has three ex'citin tion is shownin Fig. 11.

ed in each end of the stator frame 15 and serves the double functions of the plates 27 and 30 hereinbefore described. It will be evident that four different paths are provided in this-machine for the exciting flux, and these can be 'deslgned with regard only to maximum strength, since only a relatively small portion of the total flux will pass through the narrow parts of the inductors' This coils 16, whose arrangement is substantial y the same as in the machines of Figs. 6 and 9.

A modified form of alternator of the cylindrical inductor type of m present invenn this machine, I employed an inductor disc 23" of maximum strength and minimum dead weight, and the construction is such that no flux is carried through the body of the inductor or throughany auxiliary stator member. This is made possible by the use of a laminted armature core of special construction. The armature core is divided into two parts 18* and 18 and these two parts are separatedby a ring 35 of non-magnetic material. The

slots in the double core parts 18 and 18 are continuous and also extend through the non-magnetic ring 35, and the armature winding consists of conductors passing through the laminated structiire as a whole.

The field winding 16 is positioned in such a way that the exciting flux passes from the laminated armature core part 18* into the inductor at one side of the nonmagnetic ring 35and back through the inductor on the-other side of the ring 35 to the armature core part 18. If themagnetic poles of the inductor extend entirely across its cylindri cal surface, electromotive forces induced in the two halves of each armature conductor will neutralize. For this reason the mag netic poles are relatively offset in the'two halves of the cylindrical surface of the inductor, so that a slot anditsnon-magnetic filling block 25 in one half are opposite the magnetic tooth 24 in the other half. The ex citing flux thus passes only through the enlarged or flared peripheral portion of the inductor. In Fig. 12 I have illustrated a;

machine having four inductor discs 23" mounted on the same shaft 19. This machine consists in effect of four separate maaths are such that the inductor chines embodying. the principles of the ma chine of Fig; 11 mounted in a single stator frame 15.

Fig. 13 represents a machine of the type of Fig. 11 having two inductors 23. This machme has a single exciting coil 16 mounted between the ring-shaped members 21 and operates in part like the machine of Fig. 1.

That is to say, a portion of the exciting flux in the machine of Fig. 13 passes through the body of both inductors. In addition, this machine has a two part armature core 18-18 separated by a non-magnetic ring 35. The peripheries of the two inductors 23 are so close together that a portion of the exciting flux passes from one inductor to the other across the air gap between the adjaby temperature rises, it is sometimes diflicult to maintain a small air gap. Where the laminated armature core is mounted directly on the stator frame, as in all the machines hereinhefore described, the laminations will expand radially upon an increase in temperature, and if the solid stator frame does not increase much in temperature while the laminated armature core becomes relatively hot, the width of the active air gap may decrease. The diameter of the inductor disc always increases upon an increase of temperature, and thus there is danger of the active air gap becoming closed by the combined expansions. One means of partly overcoming this difficulty is shown in Fig. 1a of the drawings, and depends for its operation upon the assumption that the laminated core and the inductor disc are approximately equally hot. The laminated armature core parts 18 and 18 are supported in a steel shell 40 which is flexibly secured to ringshaped members 41 by resilient members 42. The resilient members 42 are of such a degree of flexibility as to permit the steel shell 40 to decrease the width of the air gap between the shell and the members 41. The steel shell readily absorbs heat from the laminated core parts 18 and 18 and its resultant expansion decreases the width of the air gap between the shell and the ringshaped member 421, and at the same time increases the inner diameter of the laminated armature core to compensate for an increased diameter of the inductor on account of its expansion as the result of a similar temperature rise.

The alternator of my present invention is particularly adapted for the development of alternating current of radio frequency, that is to say alternating current of that frequency adapted for radio communication. it will of course be understood that the cylindrical peripheral surface of the inductor is provided With very large number of uniformly distributed slots with a correspondingly large number of magnetic poles, and the reldimensions of Fig. 52 of the drawings are not to be considered as representative, since the dimensions of this figure are arbitrarily chosen entirely for explanatory purposes. While I have illustrated in Fig. 15 a zig-zag t pe of armature winding, it will of course he understood that many other types of windings may be employed, and when a machine has two or more independent armaturecircuits, these circuits may be connected in series or parallel, as desired.

I have explained my invention by illustrating and describing certain particular embodiments thereof, but it will be readily understood by those skilled in the art that the invention may be embodied in other forms. I, accordingly, do not wish to be restricted to the particular constructions disclosed herein by way of example for the purpose of setting forth my invention in accordance with the patent statutes, but I aim in the appended claims to cover all changes and modifications within the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is,-

l. A high frequency alternator comprising a plurality of rotatable disc-shaped magnetic inductors terminating at their outer peripheries in cylindrical surfaces and adapted to be driven at high speeds, each of said cylindrical surfaces having a plurality of uniformly distributed slots, non-magnetic material secured in said slots flush with the cylindrical surfaces, a stationary core of laminated magnetic material surrounding the cylindrical surfaces of said inductors and separated therefrom by small air gaps, said stationary core having a plurality of uniformly distributed transverse slots on its inner surface, armature conductors positioned in said last mentioned slots, and exciting windings adapted to set up an exciting flux across said air gaps, said inductors and stationary core being so related as to form a plurality of substantially separate magnetic circuits through which the flux produced by said winding will flow.

2. A high frequency alternator comprising a rotatable disc-shaped magnetic inductor terminating at its outer periphery in a cylindrical surface and adapted to be driven at high speed, said cylindrical surface having a plurality of uniformly distributed slots, non-magnetic material filling said slots, a stationary core of laminated magnetic material surrounding the cylindrical surface of said inductor and separated therefrom by a small air gap, an armature winding carried by said core, exciting Windings, and means including a plurality of stationary magnetic members separated from said inductor by small air gaps for providing a plurality of substantially separate magnetic cirpuits for the flux produced by the current in said exciting windripheral surface, non-magnetic material filling the slots in the cylindrical surface of each of said inductors thereby providing alternate segments of magnetic and non-magnetic material, a stationary magnetic member between said inductors, a stationary core of laminated magnetic material surrounding the cylindrical surface of each inductor and separated therefrom by a small air gap, armature conductors carried by each of said cores, an exciting winding, and means whereby the flux set up bytthe current flowing in' said excitin winding enters the cylindrical periphera surface of one inductor in one direction, passes through said stationmagnetic member and leaves the cylindrical peripheral surface of the other inductor in the opposite direction.

4.,A high frequency alternator comprising a plurality of disc-shaped ma netic'inductors mounted on a common s aft and.

adapted to be rotated at high speed, each of said inductors having a slotted cylindrical peripheral surface, non-magnetic material fillin the slots in the cylindrical surface of eac of said inductors thereb providing alternate segments of magnetlc and non-magnetic materials, a stationary core of laminated magnetic material surrounding the cylindrical surface of each inductor and separated therefrom by a small air gap, a stationary magnetic member separated from two of said inductors by small air gaps and adapted to provide a magnetic circuit from one inductor to the other, and

' one of which surrounds the cylindrical surface of each inductor and separated therefrom by a small air gap,armature conductors carried by each of said'co'res, and a stationary magnetic member separated from eachof said inductors by a small air ga and adapted to provide a magnetic circult from one inductor to the other.

6. A high frequency alternator comprising a rotatable disc-shaped magnetic inductor terminatin at its outer periphery in a cylindrical sur ace and adapted to be driven at high speed,said cylindrical surface having a plurality of uniformly distributed slots, nonmagnetic material secured in said slots flush with said cylindrical surface, a stationary core of laminated magnetic material surrounding the cylindrical surface of said inductor and separated therefrom by a small air gap, an armature winding carried by said core, a stator frame of magnetic material, an exciting winding mounted on said frame, and a pair of stationary magnetic members extending from said frame on opposite sides of said inductor and separated from said inductor by small air gaps.

7 A high frequency alternator comprising a rotatable magnetic inductor terminating at its outer periphery in a'cylindrical surface and adapted to be driven at high speed, said cylindrical surface having a. plurality of distributedslots, non-magnetic material filling said slots, a stationary magnetic core surrounding the cylindrical surface of said inductor and separated therefrom by a small air gap, an armature winding carried by said core, a second cylindrical surface on said inductor concentric with the outer periphery of the inductor, a stationary magnetic member separated from the second cylindrical surface of said inductor by a small air gap, and an exciting winding positioned so that the flux set up thereby crosses said two air gaps in relatively opposite directions.

8. A high frequency alternator comprising a rotatable magnetic inductor terminating at its 'outerperiphery in a cylindrical surface and adapted to be driven at high s ed, said cylindrical surface having a plural ty of distributed slots, non-magnetic material filling said slots, a stationary magnetic core surrounding the cylindrical surface of said inductor and separated therefrom by a small air gap. an armature winding carried by said core, said inductor having a pair of second cylindrical surfaces of smaller diameter than its peripheral surface, stationary magnetic gap, an armature winding carried by said core, a pair of stationary magnetic members separated from the other cylindrical surfaces ing positioned so that the flux set up there- 1 by passes across both of said air gaps.

10. A high frequency alternator comprising a plurality of magnetic inductors mounted on a common shaft and adapted to be rotated at high speed, each of said inductors having a slotted cylindrical peripheral surface, non-magnetic material secured in the slots flush with the cylindrical surface of each of said inductors, and a magnetizing winding, said inductors being assembled on said shaft in two groups so that the magnetic flux set up by said magnetizing winding enters the cylindrical surfaces of one group of inductors in one direction and leaves through the corresponding cylindrical surfaces of the other group of inductors in the opposite direction.

11. A high frequency alternator comprisiny hand this 22nd da ing a rotor of the inductor type having a two-part continuous cylindrical peripheral surface, each part of said cylindrical peripheral surface being slotted in such a manner that the slots in one part are opposite the teeth in the other part, non-magnetic material secured in said slots flush wlth said cylindrical surface, a magnetic core surrounding said cylindrical peripheral surface and separated therefrom by a small air gap, armature conductors carried by said core, and a magnetizing Winding adapted to set up a flux which passes into the inductor across the air gap adjacent one part of its cylindrical surface and leaves the inductor across the air gap adjacent the other part of its cylindrical surface.

-In witness whereof I have hereunto set of Se tember, 1916. ERNST F. W. AlEXAJ. DERSO'N. 

